1. Field of the Invention
The present disclosure relates to a mobile terminal which can improve wireless charging efficiency and reduce heat generation by adjusting the saturation magnetic flux density and eddy currents of a shield sheet, and particularly, to a wireless charging module therefor.
2. Background of the Invention
Recently, mobile terminals allowing users to receive broadcast or multicast signals to view video or television programs have created the demand for higher-capacity batteries. However, batteries having a satisfactory level of capacity have not been developed yet despite continuing research. As a result, unless a charging operation is performed by determining a proper charging time and method based on a residual battery amount, mobile terminals may often fail to allow user to view video or television programs.
Accordingly, a variety of charging apparatuses and methods for making it easy to charge a battery of a mobile terminal are being developed.
In general, in order to charge a battery, there is a need for a charging unit (or charging body or charging apparatus) connected to a general power source to supply electric energy to a battery of a mobile terminal. Separate contact terminals are respectively provided to outsides of the charging unit and the battery so that the battery can be charged by connecting both contact terminals.
However, the contact terminals provided to outsides of the charging unit and the battery are not desirable in terms of appearance. Moreover, if they are exposed to moisture, the charged energy may be lost, and a charging operation may not be properly performed due to an inferior contact status. Further, the user needs to always carry the charging unit in order to charge the battery.
Therefore, to solve the above-mentioned problems, there has been developed a method that allows easy charging in a wireless (or contactless) manner without including separate contact terminals respectively in the charging unit and the battery, which is used in some fields of applications.
Known examples of the conventional non-contact charging method include a wireless charging method using inductive coupling and a wireless charging method using capacity coupling. Of the two methods, the wireless charging method using inductive coupling is a method in which a charging unit (e.g., charging pad) is equipped with a primary coil (transmission coil) and a charging target such as a terminal is equipped with a secondary coil (reception coil), and a current generated by the inductive coupling between the primary and secondary coils when the terminal approaches the charging unit is converted into energy to charge a battery.
The secondary coil has an elliptical shape and is provided on the rear surface of the mobile terminal, i.e., on the inside of a battery case, a rectangular-shaped shield sheet for shielding a magnetic flux generated by the secondary coil by electromagnetic induction is positioned under the secondary coil, and a battery cover is placed on top of the secondary coil. That is, if the battery cover is closed, the shield sheet, the secondary coil, and the battery cover are arranged in order from the inside to the outside.
In the non-contact charging method using inductive coupling, however, the secondary coil causes a magnetic flux density to quickly reach a saturated state in the case of wireless charging because the shield sheet is formed in a simple rectangular shape, and the magnetic flux generates eddy currents in the shield sheet to disturb a change in magnetic field.
Therefore, unsaturated magnetic fields of the secondary coil (reception coil) are all lost after the magnetic flux density reaches the saturated state, whereby wireless charging efficiency is reduced, and the temperature of the shield sheet rises due to the eddy currents.